2,199 research outputs found
A tool-mediated cognitive apprenticeship approach for a computer engineering course
Teaching database engineers involves a variety of learning activities. A strong focus is on practical problems that go beyond the acquisition of knowledge. Skills and experience are equally important. We propose a virtual apprenticeship model for the knowledge- and skillsoriented Web-based education of database students. We adapt the classical cognitive apprenticeship theory to the Web context utilising scaffolding and activity theory. The choice of educational media and the forms of student interaction with the media are central success criteria
An increase in under hydrostatic pressure in the superconducting doped topological insulator NbBiSe
We report an unexpected positive hydrostatic pressure derivative of the
superconducting transition temperature in the doped topological insulator \NBS
via SQUID magnetometry in pressures up to 0.6 GPa. This result is contrary
to reports on the homologues \CBS and \SBS where smooth suppression of is
observed. Our results are consistent with recent Ginzburg-Landau theory
predictions of a pressure-induced enhancement of in the nematic
multicomponent state proposed to explain observations of rotational
symmetry breaking in doped BiSe superconductors.Comment: 5 pages, 5 figure
Herschel Observations of Cataclysmic Variables
We have used the PACS instrument on the Herschel Space Observatory to observe eight cataclysmic variables at 70 and 160 Όm. Of these eight objects, only AM Her was detected. We have combined the Herschel results with ground-based, Spitzer, and WISE observations to construct spectral energy distributions for all of the targets. For the two dwarf novae in the sample, SS Cyg and U Gem, we find that their infrared luminosities are completely dominated by their secondary stars. For the two highly magnetic "polars" in our survey, AM Her and EF Eri, we find that their mid-infrared excesses, previously attributed to circumbinary dust emission, can be fully explained by cyclotron emission. The WISE light curves for both sources show large, orbitally modulated variations that are identically phased to their near-IR light curves. We propose that significant emission from the lowest cyclotron harmonics (n †3) is present in EF Eri and AM Her. Previously, such emission would have been presumed to be optically thick, and not provide significant orbitally modulated flux. This suggests that the accretion onto polars is more complicated than assumed in the simple models developed for these two sources. We develop a model for the near-/mid-IR light curves for WZ Sge with an L2 donor star that shows that the ellipsoidal variations from its secondary star are detected. We conclude that none of the targets surveyed have dusty circumbinary disks
Factorized Q-Learning for Large-Scale Multi-Agent Systems
Deep Q-learning has achieved significant success in single-agent decision
making tasks. However, it is challenging to extend Q-learning to large-scale
multi-agent scenarios, due to the explosion of action space resulting from the
complex dynamics between the environment and the agents. In this paper, we
propose to make the computation of multi-agent Q-learning tractable by treating
the Q-function (w.r.t. state and joint-action) as a high-order high-dimensional
tensor and then approximate it with factorized pairwise interactions.
Furthermore, we utilize a composite deep neural network architecture for
computing the factorized Q-function, share the model parameters among all the
agents within the same group, and estimate the agents' optimal joint actions
through a coordinate descent type algorithm. All these simplifications greatly
reduce the model complexity and accelerate the learning process. Extensive
experiments on two different multi-agent problems demonstrate the performance
gain of our proposed approach in comparison with strong baselines, particularly
when there are a large number of agents.Comment: 7 pages, 5 figures, DAI 201
FRW Quantum Cosmology with a Generalized Chaplygin Gas
Cosmologies with a Chaplygin gas have recently been explored with the
objective of explaining the transition from a dust dominated epoch towards an
accelerating expansion stage. We consider the hypothesis that the transition to
the accelerated period involves a quantum mechanical process. Three physically
admissible cases are possible. In particular, we identify a minisuperspace
configuration with two Lorentzian sectors, separated by a classically forbidden
region. The Hartle-Hawking and Vilenkin wave functions are computed, together
with the transition amplitudes towards the accelerating epoch. Furthermore, it
is found that for specific initial conditions, the parameters characterizing
the generalized Chaplygin gas become related through an expression involving an
integer . We also introduce a phenomenological association between some
brane-world scenarios and a FRW minisuperspace cosmology with a generalized
Chaplygin gas. The aim is to promote a discussion and subsequent research on
the quantum creation of brane cosmologies from such a perspective. Results
suggest that the brane tension would become related with generalized Chaplygin
gas parameters through another expression involving an integer.Comment: 13 pages, 3 figures, RevTeX
Quantum cosmological Friedman models with a massive Yang-Mills field
We prove the existence of a spectral resolution of the Wheeler-DeWitt
equation when the matter field is provided by a massive Yang-Mills field. The
resolution is achieved by first solving the free eigenvalue problem for the
gravitational field and then the constrained eigenvalue problem for the
Yang-Mills field. In the latter case the mass of the Yang-Mills field assumes
the role of the eigenvalue.Comment: 16 pages, v3: typos corrected, final version, to appear in CQ
Late 20th Century Indian Ocean Heat Content Gain Masked by Wind Forcing
Rapid increases in upper 700âm Indian Ocean heat content (IOHC) since the 2000s have focused attention on its role during the recent global surface warming hiatus. Here, we use ocean model simulations to assess distinct multidecadal IOHC variations since the 1960s and explore the relative contributions from wind stress and buoyancy forcing regionally and with depth. Multidecadal wind forcing counteracted IOHC increases due to buoyancy forcing from the 1960s to the 1990s. Wind and buoyancy forcing contribute positively since the midâ2000s, accounting for the drastic IOHC change. Distinct timing and structure of upper ocean temperature changes in the eastern and western Indian Ocean are linked to the pathway how multidecadal wind forcing associated with the Interdecadal Pacific Oscillation is transmitted and affects IOHC through local and remote winds. Progressive shoaling of the equatorial thermoclineâof importance for lowâfrequency variations in Indian Ocean Dipole occurrenceâappears to be dominated by multidecadal variations in wind forcing
Image and Information Fusion Experiments with a Software-Defined Multi-Spectral Imaging System for Aviation and Marine Sensor Networks
The availability of Internet, line-of-sight and satellite identification and surveillance information as well as low-power, low-cost embedded systems-on-a-chip and a wide range of visible to long-wave infrared cameras prompted Embry Riddle Aeronautical University to collaborate with the University of Alaska Arctic Domain Awareness Center (ADAC) in summer 2016 to prototype a camera system we call the SDMSI (Software-Defined Multi-spectral Imager). The concept for the camera system from the start has been to build a sensor node that is drop-in-place for simple roof, marine, pole-mount, or buoy-mounts. After several years of component testing, the integrated SDMSI is now being tested, first on a roof-mount at Embry Riddle Prescott. The roof-mount testing demonstrates simple installation for the high spatial, temporal and spectral resolution SDMSI. The goal is to define and develop software and systems technology to complement satellite remote sensing and human monitoring of key resources such as drones, aircraft and marine vessels in and around airports, roadways, marine ports and other critical infrastructure. The SDMSI was installed at Embry Riddle Prescott in fall 2016 and continuous recording of long-wave infrared and visible images have been assessed manually and compared to salient object detection to automatically record only frames containing objects of interest (e.g. aircraft and drones). It is imagined that ultimately users of the SDMSI can pair with it via wireless to browse salient images. Further, both ADS-B (Automatic Dependent Surveillance-Broadcast) and S-AIS (Satellite Automatic Identification System) data are envisioned to be used by the SDMSI to form expectations for observing in future tests. This paper presents the preliminary results of several experiments and compares human review with smart image processing in terms of the receiver-operator characteristic. The system design and software are open architecture, such that other researchers are encouraged to construct and participate in sharing results and networking identical or improved versions of the SDMSI for safety, security and drop-in-place scientific image sensor networking
Heterogeneous cavitation from atomically smooth liquid-liquid interfaces
Pressure reduction in liquids may result in vaporization and bubble
formation. This thermodynamic process is termed cavitation. It is commonly
observed in hydraulic machinery, ship propellers, and even in medical therapy
within the human body. While cavitation may be beneficial for the removal of
malign tissue, yet in many cases it is unwanted due to its ability to erode
nearly any material in close contact. Current understanding is that the origin
of heterogeneous cavitation are nucleation sites where stable gas cavities
reside, e.g., on contaminant particles, submerged surfaces or shell stabilized
microscopic bubbles. Here, we present the finding of a so far unreported
nucleation site, namely the atomically smooth interface between two immiscible
liquids. The non-polar liquid of the two has a higher gas solubility and acts
upon pressure reduction as a gas reservoir that accumulates at the interface.
We describe experiments that clearly reveal the formation of cavitation on
non-polar droplets in contact with water and elucidate the working mechanism
that leads to the nucleation of gas pockets through simulations.Comment: This preprint has not undergone peer review or any post-submission
improvements or corrections. The Version of Record of this article is
published in Nature Physics, and is available online at
https://doi.org/10.1038/s41567-022-01764-
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